King is not even allowing people to sign up for health coverage online without assistance at first; they will have to go through an insurance agent or a community group until at least mid-October.

Tuesday is the long-awaited kickoff for President Obama’s signature health care law, when millions of Americans can start signing up for new insurance options. Yet across the country, officials are issuing warnings that despite fevered efforts, their new insurance exchanges — online markets where people can shop for health plans and see if they qualify for federal subsidies — will not be fully operational for weeks or even months.

Last week, the District of Columbia’s exchange announced that it would not immediately be able to determine online whether people qualify for Medicaid, which about half the states are expanding under the law, or for a federal subsidy to help cover the cost of private coverage. In Colorado, for the first month, people who want to know if they are eligible for a subsidy will have to call a customer-service line.

In Nevada, home to a large Hispanic population, a Spanish-language version of the exchange website will not be ready until mid-November. And in Maryland, small businesses will not be able to buy insurance for their employees through the state exchange until January. Federally run exchanges are having similar problems.

Now many of the 16 directors of state-run exchanges are describing October as a “soft launch” period, when Americans can start exploring their coverage options — but on websites that may be incomplete, vulnerable to glitches, and perhaps not ready for a full onslaught of customers.

“I have no idea what this thing’s going to look like on Oct. 1,” King said one afternoon last week as dozens of tense-looking programmers on laptops, scattered through the exchange offices outside Portland, rushed to finish testing and fix problems. “We could crash and burn and have to close it down.”

The outcome could hardly be more important for Obama. With Republicans threatening to shut down the government unless Democrats agree to delay the law for a year, even small problems with the exchanges could be powerful fodder for the law’s opponents.

Any insurance coverage acquired through the exchanges will not take effect until Jan. 1, when the health care law will start requiring most Americans to have insurance or to pay a tax penalty. Ferguson and other officials are predicting that while people might flood the exchange websites in October to learn about their options, few will actually enroll so soon.

To be covered starting Jan. 1, people need to sign up for coverage through the exchanges by Dec. 15.

“The idea that huge numbers are in essence going to do layaway purchasing three months out, I just think runs against the American way,” Ferguson said.

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